It will be shown that the nucleation kinetics of silver loaded inks is identical to that of deionized water. The nucleation response of the silver-loaded inks described in this patent specification is also indistinguishable from aqueous inks formulated with dye and pigment colorants. It will be further shown that the nucleation kinetics of all the aforementioned liquids can be described as a function of heater power per unit volume.
Thus the results are applicable to any heater size, shape, thin film stack, or print head manufacturer. The discovery that heavily loaded conductive silver inks have the same nucleation kinetics as common water and ordinary reflection print inks was unexpected.
Another unexpected discovery was that inks heavily loaded with silver have low viscosity. With up to 27 wt. % of the liquid consisting of solid metal particles, it was surprising to see that the conductive inks had viscosity values between 2.25 and 2.72 mPa-s. In other words, heavily loaded silver inks can be formulated to attain viscosity values on par with typical thermal inkjet inks.
With regards to nucleation kinetics, two applicable prior art patents are U.S. Pat. No. 6,132,030 issued Oct. 17, 2000, to Robert W. Cornell, as inventor of this application, and U.S. Pat. No 6,575,563 issued Jun. 120, 2003, also to Robert W. Cornell. The U.S. Pat. No. 6,132,030 describes a method of printing with a thermal inkjet printhead whereby the power per unit heater area is greater than 2 gigawatts per square meter. The U.S. Pat. No. 6,575,563 extends the teachings to include various thin film materials and thickness values. It describes the advantages of maintaining the heater-stack power per unit volume to values greater than 1.5×1015 Watts per cubic meter. Both of these patents were based upon laboratory experiments involving traditional dye and pigment colorant inks, i.e. aqueous inks that were designed for reflection print metrics like gamut, optical density and light fastness, not electrical conductivity.